D. Colette Williams

Comparable myelinated nerve pathology in feline and human diabetes mellitus

The occurrence of diabetic neuropathy in cats provides an opportunity to study the development and treatment of neurological complications not present in diabetic rodent models, where few pathological alterations are evident. The present study further defines pathological alterations in nerve biopsies from 12 cats with spontaneously occurring diabetes mellitus. Peroneal nerve biopsies displayed concurrent injury to both Schwann cells and axons of myelinated fibers that was remarkably similar to that present in human diabetic neuropathy. In addition to demyelination, remyelination (constituting 20–84% of the total myelinated fiber population) was indicated by fibers with inappropriately thin myelin sheaths. Unlike our previous investigations, striking axonal injury was apparent, and consisted of dystrophic accumulations of membranous debris or neurofilaments, as well as degenerative fiber loss resulting in a 50% decrease in myelinated fiber density. In spite of extensive fiber loss, regenerative clusters were apparent, suggesting that axonal regeneration was not completely frustrated. These data highlight the potential utility of feline diabetic neuropathy as a model that faithfully replicates the nerve injury in human diabetes mellitus.

LG2 agrin mutation causing severe congenital myasthenic syndrome mimics functional characteristics of non-neural (z−) agrin

We describe a severe form of congenital myasthenic syndrome (CMS) caused by two heteroallelic mutations: a nonsense and a missense mutation in the gene encoding agrin (AGRN). The identified mutations, Q353X and V1727F, are located at the N-terminal and at the second laminin G-like (LG2) domain of agrin, respectively. A motor-point muscle biopsy demonstrated severe disruption of the architecture of the neuromuscular junction (NMJ), including: dispersion and fragmentation of endplate areas with normal expression of acetylcholinesterase; simplification of postsynaptic membranes; pronounced reduction of the axon terminal size; widening of the primary synaptic cleft; and, collection of membranous debris material in the primary synaptic cleft and in the subsynaptic cytoplasm. Expression studies in heterologous cells revealed that the Q353X mutation abolished expression of full-length agrin. Moreover, the V1727F mutation decreased agrin-induced clustering of the acetylcholine receptor (AChR) in cultured C2 muscle cells by >100-fold, and phosphorylation of the MuSK receptor and AChR beta subunit by ~tenfold. Surprisingly, the V1727F mutant also displayed increased binding to α-dystroglycan but decreased binding to a neural (z+) agrin-specific antibody. Our findings demonstrate that agrin mutations can associate with a severe form of CMS and cause profound distortion of the architecture and function of the NMJ. The impaired ability of V1727F agrin to activate MuSK and cluster AChRs, together with its increased affinity to α-dystroglycan, mimics non-neural (z−) agrin and are important determinants of the pathogenesis of the disease.

Juvenile idiopathic Epilepsy in Egyptian Arabian foals: 22 cases (1985-2005)

BACKGROUND Epilepsy is relatively uncommon in horses compared with other species and limited information is available. HYPOTHESIS The objectives of the study were to describe the age of onset, clinical signs, clinicopathologic data, electroeticephalographic findings, treatment, and outcome, including long-term prognosis in Arabian foals with idiopathic epilepsy. ANIMALS Twenty-two foals were included in the study. MATERIALS AND METHODS Medical records from 1985 to 2005 were reviewed. RESULTS The age of onset of affected foals ranged from 2 days to 6 months. Seizures were characterized by generalized tonic and clonic motor activity, staring, and loss of consciousness. The most common postictal signs were transient blindness and abnormal mental status. The interictal neurologic examination was otherwise normal. Clinicopathologic data and imaging diagnostics were normal except in 4 foals that developed complications. Electroencephalography revealed epileptiform activity in 9 of 13 foals. Foals were treated with benzodiazepines for the short-term; whereas phenobarbital was used over the long-term. Potassium bromide was added in 3 foals in which seizures were multiple, frequent, and difficult to control. The long-term prognosis was favorable with cessation of seizures by 1 year of age. The most common complication was head trauma. The most common concurrent disease was pneumonia. CONCLUSIONS AND CLINICAL IMPORTANCE Juvenile idiopathic epilepsy of Egyptian Arabian foals has an early clinical onset but appears to be self-limiting. Information obtained from this study strongly suggests a heritable condition that merits further investigation.

Development of an avian brachial plexus nerve block technique for perioperative analgesia in mallard ducks (Anas platyrhynchos).

Abstract Surgical procedures of the wing are commonly performed in companion, captive, and wild avian species. To develop a clinically applicable brachial plexus nerve block technique for perioperative analgesia in birds, 8 adult female mallard ducks (Anas platyrhynchos) were anesthetized and used in several local anesthetic trials with bupivacaine (2 or 8 mg/kg) or a combination of lidocaine (15 mg/kg) and epinephrine (3.8 µg/kg) perineurally; equal volumes of saline were administered as control treatments. Both axillary and dorsal approaches to the brachial plexus were evaluated. With the axillary approach, radial and ulnar compound nerve action potentials (CNAP), sensory nerve conduction velocities (SNCVs), and cord dorsum potentials (CDPs) were recorded after distal sensory nerve stimulation. Values were recorded before and at 5, 30, and 60 minutes after injection of local anesthetic or saline. Birds were monitored for the presence of a wing droop and a change in motor function on recovery from anesthesia. Results were highly variable for all techniques. No technique significantly decreased CDPs or resulted in consistent wing droop. Radial and ulnar CNAPs, SNCVs, and CDPs were consistently recorded in all birds. Variable results might indicate that the treatment, concentration, or volume of local anesthetic used was ineffective in producing local anesthesia. Electrodiagnostic methods used in these ducks to assess loss of sensory nerve conduction might not be sensitive enough to assess the effects of local anesthesia. Further research is needed to identify methods for assessing the efficacy of brachial plexus nerve blockade in birds.

Evaluation of deafness in American Paint Horses by phenotype, brainstem auditory-evoked responses, and endothelin receptor B genotype

OBJECTIVE To evaluate deafness in American Paint Horses by phenotype, clinical findings, brainstem auditory-evoked responses (BAERs), and endothelin B receptor (EDNBR) genotype. DESIGN Case series and case-control studies. ANIMALS 14 deaf American Paint Horses, 20 suspected-deaf American Paint Horses, and 13 nondeaf American Paint Horses and Pintos. PROCEDURES Horses were categorized on the basis of coat color pattern and eye color. Testing for the EDNBR gene mutation (associated with overo lethal white foal syndrome) and BAERs was performed. Additional clinical findings were obtained from medical records. RESULTS All 14 deaf horses had loss of all BAER waveforms consistent with complete deafness. Most horses had the splashed white or splashed white-frame blend coat pattern. Other patterns included frame overo and tovero. All of the deaf horses had extensive head and limb white markings, although the amount of white on the neck and trunk varied widely. All horses had at least 1 partially heterochromic iris, and most had 2 blue eyes. Ninety-one percent (31/34) of deaf and suspected-deaf horses had the EDNBR gene mutation. Deaf and suspected-deaf horses were used successfully for various performance events. All nondeaf horses had unremarkable BAER results. CONCLUSIONS AND CLINICAL RELEVANCE Veterinarians should be aware of deafness among American Paint Horses, particularly those with a splashed white or frame overo coat color pattern, blend of these patterns, or tovero pattern. Horses with extensive head and limb markings and those with blue eyes appeared to be at particular risk.

Gender effects in hearing loss in Dalmatians.

Brainstem auditory-evoked-response data were collected from 3101 Dalmatian dogs from 1984 to 1998 at the Veterinary Medicine Teaching Hospital at the University of California, Davis. Also collected were data on eye color and the presence or absence of a color-patch at birth. Our objective was to evaluate the role of gender in hearing loss, including the possibility that the probability of suffering unilateral or bilateral deafness was greater if the dam was hearing impaired than if the sire was hearing impaired. Results of a multiple-trait threshold-model analysis support the commonly held observation that females were more likely to be deaf than males. In addition, females were also more likely to have two blue eyes (a condition associated with an increased prevalence of deafness). However, gender differences in hearing loss were limited to these direct observations. There was no detectable difference in the prevalence of hearing loss between offspring of deaf mothers and the offspring of deaf fathers. Finally, there was no detectable decrease in the prevalence of hearing loss over the years covered in the data set - suggesting that Dalmatian breeders are not yet selecting against hearing problems.

COLQ variant associated with Devon Rex and Sphynx feline hereditary myopathy

Summary Some Devon Rex and Sphynx cats have a variably progressive myopathy characterized by appendicular and axial muscle weakness, megaesophagus, pharyngeal weakness and fatigability with exercise. Muscle biopsies from affected cats demonstrated variable pathological changes ranging from dystrophic features to minimal abnormalities. Affected cats have exacerbation of weakness following anticholinesterase dosing, a clue that there is an underlying congenital myasthenic syndrome (CMS). A genome‐wide association study and whole‐genome sequencing suggested a causal variant for this entity was a c.1190G>A variant causing a cysteine to tyrosine substitution (p.Cys397Tyr) within the C‐terminal domain of collagen‐like tail subunit (single strand of homotrimer) of asymmetric acetylcholinesterase (COLQ). Alpha‐dystroglycan expression, which is associated with COLQ anchorage at the motor end‐plate, has been shown to be deficient in affected cats. Eighteen affected cats were identified by genotyping, including cats from the original clinical descriptions in 1993 and subsequent publications. Eight Devon Rex and one Sphynx not associated with the study were identified as carriers, suggesting an allele frequency of ~2.0% in Devon Rex. Over 350 tested cats from other breeds did not have the variant. Characteristic clinical features and variant presence in all affected cats suggest a model for COLQ CMS. The association between the COLQ variant and this CMS affords clinicians the opportunity to confirm diagnosis via genetic testing and permits owners and breeders to identify carriers in the population. Moreover, accurate diagnosis increases available therapeutic options for affected cats based on an understanding of the pathophysiology and experience from human CMS associated with COLQ variants.

A COLQ Missense Mutation in Labrador Retrievers Having Congenital Myasthenic Syndrome

Congenital myasthenic syndromes (CMSs) are heterogeneous neuromuscular disorders characterized by skeletal muscle weakness caused by disruption of signal transmission across the neuromuscular junction (NMJ). CMSs are rarely encountered in veterinary medicine, and causative mutations have only been identified in Old Danish Pointing Dogs and Brahman cattle to date. Herein, we characterize a novel CMS in 2 Labrador Retriever littermates with an early onset of marked generalized muscle weakness. Because the sire and dam share 2 recent common ancestors, CMS is likely the result of recessive alleles inherited identical by descent (IBD). Genome-wide SNP profiles generated from the Illumina HD array for 9 nuclear family members were used to determine genomic inheritance patterns in chromosomal regions encompassing 18 functional candidate genes. SNP haplotypes spanning 3 genes were consistent with autosomal recessive transmission, and microsatellite data showed that only the segment encompassing COLQ was inherited IBD. COLQ encodes the collagenous tail of acetylcholinesterase, the enzyme responsible for termination of signal transduction in the NMJ. Sequences from COLQ revealed a variant in exon 14 (c.1010T>C) that results in the substitution of a conserved amino acid (I337T) within the C-terminal domain. Both affected puppies were homozygous for this variant, and 16 relatives were heterozygous, while 288 unrelated Labrador Retrievers and 112 dogs of other breeds were wild-type. A recent study in which 2 human CMS patients were found to be homozygous for an identical COLQ mutation (c.1010T>C; I337T) provides further evidence that this mutation is pathogenic. This report describes the first COLQ mutation in canine CMS and demonstrates the utility of SNP profiles from nuclear family members for the identification of private mutations.

Variation in Genes Related to Cochlear Biology Is Strongly Associated with Adult-Onset Deafness in Border Collies

Domestic dogs can suffer from hearing losses that can have profound impacts on working ability and quality of life. We have identified a type of adult-onset hearing loss in Border Collies that appears to have a genetic cause, with an earlier age of onset (3–5 years) than typically expected for aging dogs (8–10 years). Studying this complex trait within pure breeds of dog may greatly increase our ability to identify genomic regions associated with risk of hearing impairment in dogs and in humans. We performed a genome-wide association study (GWAS) to detect loci underlying adult-onset deafness in a sample of 20 affected and 28 control Border Collies. We identified a region on canine chromosome 6 that demonstrates extended support for association surrounding SNP Chr6.25819273 (p-value = 1.09×10−13). To further localize disease-associated variants, targeted next-generation sequencing (NGS) of one affected and two unaffected dogs was performed. Through additional validation based on targeted genotyping of additional cases (n = 23 total) and controls (n = 101 total) and an independent replication cohort of 16 cases and 265 controls, we identified variants in USP31 that were strongly associated with adult-onset deafness in Border Collies, suggesting the involvement of the NF-κB pathway. We found additional support for involvement of RBBP6, which is critical for cochlear development. These findings highlight the utility of GWAS–guided fine-mapping of genetic loci using targeted NGS to study hereditary disorders of the domestic dog that may be analogous to human disorders.

Myopathy with tubulin-reactive inclusions in two cats

Many types of inclusions have been described in human myopathies including but not limited to nemaline rod bodies, cylindrical spirals, tubular aggregates, cytoplasmic bodies, reducing bodies, and fingerprint bodies, and hyaline inclusions in myofibrillar myopathy and inclusion body myositis. There are very few reports describing inclusions in spontaneously occurring myopathies in cats, and these reports are limited to nemaline rod myopathy. A myopathy with tubulin-reactive crystalline inclusions has recently been reported in a human patient with a clinical presentation of myalgia and fatigue. Similarly, a myopathy with chronic, slowly progressive muscle weakness has been identified here in two unrelated cats. Inclusions were the only pathological change in skeletal muscle biopsies and, ultrastructurally, groups of crystalline structures were evident that had a subsarcolemmal or central location, rhomboid or rectangular shapes, lacked orientation, and were not membrane bound. The crystalline structures reacted positively with an antibody against tubulin. This feline myopathy may be the equivalent of the human myopathy with tubulin-positive crystalline inclusions.